This article is more about indoor farming than vertical farming (is it even vertical if there's only one row?). I grow lettuce indoors. It serves as a nice houseplant and fresh source of salad greens for lunch. It's fairly new, so the cost isn't that much different than just buying lettuce. Once I start building my own "pods" instead of buying the brand-name pods, though, I expect it'll be a bit cheaper than buying 4 bags of lettuce every week (although it doesn't produce enough to fully replace buying greens).

Mine produced ~4 bags over 6 weeks for an energy cost of ~$5 and a negligible amount of water. I think I can get the per-plant cost down to ~$0.50 once I start using my own seeds, so around $10 over 6 weeks to replace 4 bags of salad at around $3 each... a grand savings of $2. We're moving around 4 bags of greens a week between 2 adults, so I'd need to 6x that to replace all the greens we're eating, which gets the savings up to ~$2/week.

The cost savings is negligible -- I do it because it's neat and I like having a houseplant I can eat. It's also MUCH easier for a residential system to offset its energy usage than a commercial setup (I have way more square footage on my roof than I would ever "grow" inside my house).

The calorie argument is more compelling, but how many thousands of years did it take for people to get wheat so calorically dense? I think it's going to take time to develop nutrient-rich crops specifically tailored for indoor farming.